People living near Kings Delph said they felt angry and “sick” over the huge number of fish deaths, the foul odour and the discoloured water.
At the time, the Environment Agency said Anglian Water’s pumping station discharged for 23 hours after a pump failed.
It was classed as a “category one” incident, meaning it had a “major effect” on either water quality, human health, conservation or businesses.
The Environment Agency previously told the BBC the “complex investigation” was completed in December, with a file of evidence due to be reviewed.
After Barclay raised the lack of any prosecution in Parliament in March, Hardy said she would look into it and get back to him in writing.
On Thursday, he told the Commons that when he received no response, he had escalated the issue to the Speaker, and had then been promised an answer by 8 May.
“We’re now a further month on from that and still there has been no reply,” he said.
“So if the government has changed its policy and no longer is prosecuting the most serious water incidents then should that change of policy not be notified to the House, or is it that ministers simply, despite repeated requests, have no idea what is happening in their own department?”
Hardy apologised and said she would “follow up immediately with the department” and arrange a meeting with Barclay in the coming weeks.
“I am sorry that that has happened, it’s not acceptable and we’ll make changes to put it right,” she added.
The Environment Agency and Anglian Water, which is responsible for the dyke, have been approached for comment.
